Graphene reinforced polystyrene composite for separation of nonpolar compounds from water

ABSTRACT

A composite material of polyurethane foam having a layer of reduced graphene oxide and polystyrene is described. This composite material may be made by contacting a polyurethane foam with a suspension of reduced graphene oxide, drying, and then irradiating in the presence of styrene vapor. The composite material has a hydrophobic surface that may be exploited for separating a nonpolar phase, such as oil, from an aqueous solution.

STATEMENT REGARDING PRIOR DISCLOSURES BY THE INVENTORS

Aspects of this technology are described in the articles, Baig, N. andSaleh, T. A., “Natural-Light-Initiated 3D Macro Zigzag Architecture ofGraphene-Reinforced Polystyrene for Gravity-Driven Oil and WaterSeparation” Global Challenges, 2018, 2, 1800040, DOI:10.1002/gch2.201800040; and Baig, N. and Saleh, T. A., “Initiator-FreeNatural Light-Driven Vapor Phase Synthesis of a Porous Network of 3DPolystyrene Branched Carbon Nanofiber Grafted Polyurethane forHexane/Water Separation,” Chemistry Select 2018, 3, 8312, DOI:10.1002/slct.201801549. Each article is incorporated herein by referencein its entirety.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a composite of polystyrene grafted ontoreduced graphene oxide layered on a polyurethane foam support, a methodof making the composite, and a method of using the composite to separatenonpolar components from contaminated water.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Rapid industrialization and a fast-growing world population haveresulted in a high demand for energy. Oil spillage incidents have becomecommon due to the frequent oil movements across the world to supplythese high energy demands. The Deep-water Horizon oil spill (2010) inthe Gulf of Mexico was considered to be a major oil spillage accident inmarine water. Five million barrels of oil were released, and the deathsof 11 people were reported due to this accident. Another incident inNorth Dakota, USA in 2016 caused the release of 4,200 barrels of oil.See Z. Zhang, et al., Sci. Rep. 2018, 8, 3869. Industrial wastes mayalso contain large quantities of oil which may cause severe waterpollution if released into the environment. Oil pollution is a criticalthreat to living organisms and their ecosystem. See Y. Li, et al., Glob.Challenges 2017, 1, 1600014; and N. Cao, et al., Chem. Eng. 1 2017, 307,319. However, oil removal from water is a major challenge to maintain aclean aquatic environment. See C.-F. Wang, et al., Sci. Rep. 2017, 7,43053; and Y. S. You, et al., Sci. Rep. 2017, 7, 15345.

Oil-water separation is of great interest to the researcher due to itseconomic, social, and environmental significance. See Z. Xue, et al., J.Mater. Chem. A 2014, 2, 2445; and M. A. Riaz, et al., Environ. Sci.Pollut. Res. 2017, 24, 27731. One of the crucial factors in theperformance of the materials used for oil and water separation is theirwettability. See J. Zhang, et al., Adv. Funct. Mater. 2011, 21, 4699.Superhydrophobic surfaces can be prepared through layer by layerassembly, coating, dip-coating, drop-coating, chemical vapor deposition,and a sol-gel method. See L. Zhang, et al., Sci. Rep. 2013, 3, 2326; D.D. Nguyen, et al., Energy Environ. Sci. 2012, 5, 7908; M. Zhang, et al.,Carbohydr. Polym. 2013, 97, 59; H. Liu, et al., Langmuir 2004, 20, 5659;Z. Zhang, et al., Sci. Rep. 2018, 8, 3869; and K. Tadanaga, et al.,Chem. Mater. 2000, 12, 590. Various supports have been used to developsuperhydrophobic surfaces including mesh, sponges, foams, and fabrics.See Z. Xue, et al., Adv. Mater. 2011, 23, 4270; N. Chen, et al., ACSNano 2013, 7, 6875; X. Zhang, et al., Adv. Funct. Mater. 2013, 23, 2881;and B. Wang, et al., ACS Appl. Mater. Interfaces 2013, 5, 1827. Thehydrophobic surfaces are generated using a range of materials such asmetal, metal oxide nanoparticles, polymers, and carbon nanomaterial. SeeB. Wang, et al., ACS Appl. Mater. Interfaces 2013, 5, 1827; C. R. Crick,et al., J. Mater. Chem. A 2013, 1, 5943; C. Liu, et al., ColloidsSurfaces A Physicochem. Eng. Asp. 2015, 468, 10; and X. Gui, et al., ACSAppl. Mater. Interfaces 2013, 5, 5845. Recently, 2D graphene and itsderivatives have received extraordinary attention due to their uniquephysicochemical properties. Graphene and its derivatives are extensivelyused to improve the chemical, electrical, mechanical, and thermalbehavior of materials. See Z. Xu, et al., Glob. Challenges 2017, 1,1700050; Y. Shudo, et al., Glob. Challenges 2017, 1, 1700054; X. Liao,et al., Prog. Org. Coatings 2018, 115, 172; Y.-J. Wan, et al., Carbon N.Y. 2014, 69, 467; and N. Baig, A.-N. Kawde, Anal. Methods 2015, 7, 9535.Graphene, apart from its excellent electrochemical properties, alsopossesses remarkable hydrophobic properties. See D. D. Nguyen, et al.,Energy Environ. Sci.

2012, 5, 7908; and N. Baig, T. A. Saleh, Microchim. Acta 2018, 185, 283.The hydrophobic behavior of graphene has been exploited to fabricatehydrophobic materials for the separation of oil from water. See D. D.Nguyen, et al., Energy Environ. Sci. 2012, 5, 7908; and Y. Luo, et al.,Sci. Rep. 2017, 7, 1. For example, graphene-based hydrophobic foam canbe synthesized by a simple dip-coating method using a 3D polymerskeleton. Graphene oxide was used as a precursor to obtain graphene, andthe resulting graphene coated foam displayed good hydrophobicity. See C.Wu, et al., Adv. Mater. 2013, 25, 5658. Spongy graphene has beenobtained without any support through the hydrothermal method byenclosing graphene oxide into a sealed reactor of the desired shape andsubjecting the graphene oxide to 180° C. for 24 hours. The obtainedgraphene gel was freeze-dried for 48 hours to obtain spongy graphene.The spongy graphene had a high tendency for petroleum absorption, aswell as fat. See H. Bi, et al., Adv. Funct. Mater. 2012, 22, 4421. Inanother study, a magnetic foam was obtained by the combination ofmagnetic nanoparticles (Fe₃O₄) and graphene/reduced graphene oxide. Theintroduction of magnetic properties into the foam facilitated the facilemovement and removal of the foam after oil absorption. See C. Liu, etal., Colloids Surfaces A Physicochem. Eng. Asp. 2015, 468, 10.Similarly, a magnetic nanoparticle functionalized free standing reducedgraphene oxide foam was synthesized by the hydrothermal method. See A.Subrati, et al., Ind. Eng. Chem. Res. 2017, 56, 6945.

In most of the cases reduced graphene oxide is obtained from grapheneoxide. The synthesis and the handling of the graphene oxide arestraight-forward and cost-effective, and graphene oxide can be producedon a large scale. See D. C. Marcano, et al., ACS Nano 2010, 4, 4806.Graphene oxide has a strong hydrophilic character, and itshydrophobicity is increased by reducing it. See A. Gholampour, et al.,ACS Appl. Mater. Interfaces 2017, 9, 43275. However, the graphene oxidecannot be fully reduced, and some oxygen functionalities still remain onthe surface of the reduced graphene oxide, which prevents completehydrophobicity of the reduced graphene oxide. See N. Baig, T. A. Saleh,Microchim. Acta 2018, 185, 283. The coating of the reduced graphene on a3D support also faces the issue of long-term stability. The reducedgraphene oxide coating can deteriorate after multiple uses. Moreover,the process adapted for the production of a hydrophobic surface iseither very costly or tedious, or it is difficult to maintain a stablesurface for a long time. Another challenge is to prepare hydrophobic orhydrophilic surfaces by using readily available materials where asynthesis process is possible for the large-scale production of thehydrophobic materials. There is a need to introduce an efficienthydrophobic material which can be synthesized through a cost-effectiveprocess with a methodology that can be easily adapted for large-scaleproduction.

In view of the foregoing, a porous 3D network of polystyrene andgraphene was synthesized through a green methodology. The porous 3Dnetwork displayed excellent mechanical stability and superhydrophobicbehavior. The porous 3D network was formed using a polymerizationprocess that was carried out under natural sunlight which provided agreen, non-hazardous, and cost-effective route for the bulk productionof the superhydrophobic material with a uniform and controlledmorphology. A zigzag shaped growth of polystyrene on the surface of r-GOgrafted polyurethane of the porous 3D network was observed to provide agreater surface area for the efficient separation of oil from water.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to acomposite material, comprising a polyurethane foam coated with a layerof reduced graphene oxide (r-GO), and a layer of polystyrene in contactwith the layer of r-GO. The composite material has pore diameters in arange of 50-500 μm. In one embodiment, the composite material has anapparent contact angle with water in a range of 130°-170°.

In one embodiment, the composite material has an adsorption pore size ina range of 25-50 Å.

In one embodiment, the composite material has a BET surface area in arange of 50-100 m²/g,

In one embodiment, at least 70% of a total surface of the polyurethanefoam is coated with the layer of r-GO.

In one embodiment, at least 70% of a total exposed surface of thecomposite material is the layer of polystyrene.

According to a second aspect, the present disclosure relates to a methodof making the composite material of the first aspect, comprising thesteps of contacting a polyurethane foam with a suspension of r-GO in analcohol to produce a wet scaffold, drying the wet scaffold to produce ar-GO grafted polyurethane composite, and irradiating the r-GO graftedpolyurethane composite in the presence of a styrene vapor to produce thecomposite material.

In one embodiment, the method further comprises the step of contactingthe composite material with toluene after the irradiating.

In one embodiment, the polyurethane foam has a BET surface area in arange of 5-20 m²/g.

In one embodiment, the r-GO grafted polyurethane composite has a BETsurface area in a range of 5-20 m²/g.

In one embodiment, the r-GO is present in the suspension at aconcentration of 0.1-5 mg/mL.

In one embodiment, the contacting is done for a period of 3-60 min.

In one embodiment, the drying is at a temperature of 50-80° C. for aperiod of 6-24 h.

In one embodiment, the irradiating involves exposing the r-GO graftedpolyurethane composite to sunlight.

According to a third aspect, the present disclosure relates to a methodof separating a nonpolar compound from an aqueous solution in a mixture.This method involves contacting the mixture with the composite materialof the first aspect. The composite material adsorbs 8-25 times itsweight of the nonpolar compound.

In one embodiment, the nonpolar compound is at least one selected fromthe group consisting of hexane, heptane, toluene, xylene, and apetroleum-derived liquid.

In one embodiment, the composite material adsorbs less than 20% of itsweight of the aqueous solution.

In one embodiment, the contacting involves filtering the mixture throughthe composite material.

In one embodiment, the method further comprises the step of compressingthe composite material after the contacting to produce a dischargedcomposite material, and reusing the discharged composite material.

In one embodiment, the discharged composite material comprises at least90 wt % r-GO relative to a weight of r-GO in the composite material.

In one embodiment, the discharged composite material comprises at least90 wt % polystyrene relative to a weight of polystyrene in the compositematerial.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram showing the role of sunlight in evaporation andpolymerization of styrene.

FIG. 2 is a schematic representation of the fabrication of 3Dzz-PS/GR/PU for oil and water separation.

FIG. 3A is a FTIR spectrum of graphene.

FIG. 3B is a TEM image of graphene, scale bar 100 nm.

FIG. 4A is a SEM image of PU, scale bar 200 μm.

FIG. 4B is a higher magnification SEM image of PU, scale bar 100 μm.

FIG. 4C is a SEM image of PS/PU, scale bar 200 μm.

FIG. 4D is a higher magnification SEM image of PS/PU, scale bar 100 μm.

FIG. 4E is a SEM image of 3D zz-PS/GR/PU, scale bar 200 μm.

FIG. 4F is a higher magnification SEM image of 3D zz-PS/GR/PU, scale bar100 μm.

FIG. 5 shows FTIR spectra of PU, PS/PU, and 3D zz-PS/GR/PU.

FIG. 6A shows the BET surface areas of PU, PS/PU, and 3D zz-PS/GR/PU.

FIG. 6B shows the adsorption and desorption pore sizes of PU, PS/PU, and3D zz-PS/GR/PU.

FIG. 7A shows the growth of PS into GR/PU in the glass reactor

FIG. 7B shows the complete retention of water on the upper side of thezz-PS/GR/PU.

FIG. 7C shows the sidewise growth of PS and retention of water.

FIG. 7D shows an upper view of the zz-PS/GR/PU retaining water.

FIG. 7E is a magnified image displaying the zigzag formation of PS intoGR/PU.

FIG. 8 illustrates the separation of oil and water. A column packed with3D zz-PS/GR/PU composite is inserted into the neck of a flask (a). Amixture (b) of hexane and methylene-blue colored water is poured intothe column, and the colored water is retained while the hexane quicklypasses through the 3D zz-PS/GR/PU.

FIG. 9 is a flow chart showing the reusability of the zz-PS/GR/PU wheretoluene treated zz-PS/GR/PU (tzz-PS/GR/PU) (A) is fully compressed (B),then released (C), and still retains superhydrophobicity (D).

FIG. 10 is a graph showing the weight gain capacity of the zz-PS/GR/PUand tzz-PS/GR/PU.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

The present disclosure will be better understood with reference to thefollowing definitions. As used herein, the words “a” and “an” and thelike carry the meaning of “one or more.” Within the description of thisdisclosure, where a numerical limit or range is stated, the endpointsare included unless stated otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

As used herein, the words “about,” “approximately,” or “substantiallysimilar” may be used when describing magnitude and/or position toindicate that the value and/or position described is within a reasonableexpected range of values and/or positions. For example, a numeric valuemay have a value that is +/−0.1% of the stated value (or range ofvalues), +/−1% of the stated value (or range of values), +/−2% of thestated value (or range of values), +/−5% of the stated value (or rangeof values), +/−10% of the stated value (or range of values), +/−15% ofthe stated value (or range of values), or +/−20% of the stated value (orrange of values). Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

As used herein, “compound” is intended to refer to a chemical entity,whether as a solid, liquid, or gas, and whether in a crude mixture orisolated and purified.

As used herein, “composite” refers to a combination of two or moredistinct constituent materials into one. The individual components, onan atomic level, remain separate and distinct within the finishedstructure. The materials may have different physical or chemicalproperties, that when combined, produce a material with characteristicsdifferent from the original components. In some embodiments, a compositemay have at least two constituent materials that comprise the sameempirical formula but are distinguished by different densities, crystalphases, or a lack of a crystal phase (i.e. an amorphous phase).

For polygonal shapes, the term “diameter”, as used herein, and unlessotherwise specified, refers to the greatest possible distance measuredfrom a vertex of a polygon through the center of the face to the vertexon the opposite side. For a circle, an oval, and an ellipse, “diameter”refers to the greatest possible distance measured from one point on theshape through the center of the shape to a point directly across fromit.

The present disclosure is intended to include all hydration states of agiven compound or formula, unless otherwise noted or when heating amaterial. For example, Ni(NO₃)₂ includes anhydrous Ni(NO₃)₂,Ni(NO₃)₂.6H₂O, and any other hydrated forms or mixtures. CuCl₂ includesboth anhydrous CuCl₂ and CuCl₂.2H₂O.

In addition, the present disclosure is intended to include all isotopesof atoms occurring in the present compounds and complexes. Isotopesinclude those atoms having the same atomic number but different massnumbers. By way of general example, and without limitation, isotopes ofhydrogen include deuterium and tritium. Isotopes of carbon include ¹³Cand ¹⁴C. Isotopes of nitrogen include ¹⁴N and ¹⁵N. Isotopes of oxygeninclude ¹⁶O, ¹⁷O, and ¹⁸O. Isotopically-labeled compounds of thedisclosure may generally be prepared by conventional techniques known tothose skilled in the art or by processes analogous to those describedherein, using an appropriate isotopically-labeled reagent in place ofthe non-labeled reagent otherwise employed.

According to a first aspect, the present disclosure relates to acomposite material, comprising a polyurethane foam coated with a layerof reduced graphene oxide (r-GO), and a layer of polystyrene in contactwith the layer of r-GO.

The polyurethane foam has an average pore diameter in a range of 200-850μm, preferably 300-700 μm, more preferably 350-600 μm, though in someembodiments, a polyurethane foam having an average pore diameter of lessthan 200 μm or greater than 850 μm may be used. Here, the pore diameteris determined by SEM imaging, such as the SEM image of FIGS. 4A and 4B.In one embodiment, at least 70%, preferably at least 75%, morepreferably at least 80% of the surface of the polyurethane foam iscoated with the layer of r-GO. Here, the surface of the polyurethanefoam refers to both the interior surface (for instance, within thepores), and the exterior surface of the foam. In some embodiments, thepolyurethane foam may be considered similar to low-resilience (i.e.flexible) polyurethane, memory foam, or SORBOTHANE.

In other embodiments, materials with a similar flexibility and porosityto polyurethane foam may also be used, for instance, polyester,polystyrene, vegetal cellulose, or natural sponges. Other materialscolloquially known as “plastic foam” or “synthetic sponges” may be used.Plastic foams include ethylene-vinyl acetate (EVA) foam (formed fromcopolymers of ethylene and vinyl acetate and also referred to aspolyethylene-vinyl acetate, PEVA), low-density polyethylene (LDPE) foam,nitrile rubber foam, polychloroprene foam or NEOPRENE, polyimide foam,polypropylene (PP) foam (including expanded polypropylene andpolypropylene paper), polyethylene foam, polyvinyl chloride (PVC) foam,closed-cell PVC foam, silicone foam, and microcellular foam. Thepolyurethane foam may also be considered as a scaffold or substrate forthe r-GO.

In one preferred embodiment, the polyurethane foam has an open-cellstructure. Solid foams can be closed-cell or open-cell. In closed-cellfoam, the gas forms discrete pockets, i.e. cells, each completelysurrounded by the solid material. In open-cell foam, the cells connectto each other, and fluid paths usually exist from one side of the foamto the other side. Thus, open-cell foams may be used to filter or absorbfluids.

In one embodiment, the polyurethane foam is an open-cell foam with cellshaving an average diameter in a range of 220-900 μm, preferably 320-750μm, more preferably 370-650 μm, though in some embodiments, apolyurethane foam having an average cell diameter of less than 220 μm orgreater than 900 μm may be used. In one embodiment, the polyurethanefoam may be considered an open-cell foam despite comprising a percentageof closed cells. For instance, the polyurethane foam may comprise 1-20%,more preferably 2-16%, or 3-5% closed cells, relative to a total numberof closed cells and open cells.

In one embodiment, the polyurethane foam may comprise open cells havinga monodisperse diameter. Here, the diameter of a cell refers to thelongest length through the center of the cell. This means that the cellshave a coefficient of variation or relative standard deviation,expressed as a percentage and defined as the ratio of the cell diameterstandard deviation (σ) to the cell diameter mean (μ), multiplied by100%, of less than 25%, preferably less than 10%, preferably less than8%, preferably less than 6%, preferably less than 5%. In anotherembodiment, the cells are monodisperse having a diameter distributionranging from 80% of the average cell diameter to 120% of the averagecell diameter, preferably 85-115%, preferably 90-110% of the averagecell diameter. In another embodiment, the polyurethane foam comprisesopen cells that do not have monodisperse diameters.

In one embodiment, the polyurethane foam may comprise open cells thatare substantially rounded, meaning that the distance from the geometriccenter to anywhere defining the boundary of the cell varies by less than35%, preferably by less than 25%, more preferably by less than 20% ofthe average distance.

In general, due to the relative thinness of the layer of r-GO andpolystyrene on the polyurethane foam, the above descriptions of the cellstructure may be equally applicable to the cell structure of thecomposite material. Alternatively, one or more dimensions as discussedabove may be smaller due to the r-GO and polystyrene layer coatings. Forinstance, the composite material may have pore diameters in a range of50-500 μm, preferably 60-400 μm, more preferably 70-300 μm which may beeasily visible by SEM imaging, as of an example composite material inFIGS. 4E and 4F.

Also, the composite material may have a smaller adsorption anddesorption pore size than the polyurethane foam by itself or apolyurethane foam without r-GO and treated to the polystyrene coating.Here, the composite material has an adsorption and desorption pore sizein a range of 25-50 Å, preferably 27-45 Å, more preferably 30-40 Å, evenmore preferably 31-37 Å. In one embodiment, the adsorption pore size maybe about 34 Å, and the desorption pore size may be about 33 Å. Forcomparison, the polyurethane foam may have adsorption and desorptionpore sizes in a range of 330-380 Å.

In another embodiment, the composite material has a BET surface area ina range of 50-100 m²/g, preferably 55-80 m²/g, more preferably 60-75m²/g, or about 67 m²/g. This represents an increase in the BET surfacearea compared to the polyurethane foam by itself, which may have a BETsurface area in a range of 5-30 m²/g, 5-20 m²/g, 10-25 m²/g, 12-20 m²/g,or about 15 m²/g. A polyurethane foam without r-GO and treated with thepolystyrene coating may have a BET surface area in a range of 20-35m²/g.

In one embodiment, the composite material has an apparent contact angleof 130°-170°, preferably 140°-160°, more preferably 145°-155° with awater drop. This contact angle may be observed by placing a drop ofwater on the surface of the composite material, for instance, bypipetting 40-60 μL of water onto the composite material, or by sprayinga mist of water droplets. Preferably, a goniometer may be used tomeasure the contact angles. In another embodiment, drop sizes of 40-60μL may be used to observe contact angles The composite material may beconsidered hydrophobic or superhydrophobic, where a superhydrophobicmaterial has an apparent contact angle of 150° or greater with water.The composite material may also be considered oleophilic.

As mentioned previously, the composite material comprises a layer ofreduced graphene oxide (r-GO). Graphene oxide (GO) is an electricallyinsulating material composed of a single graphene sheet with oxygenfunctional groups bonded perpendicularly to the graphene basal-plane SeeLerf et al., “Structure of graphite oxide revisited” J. Chem. B, 102,4477 (1998). Due to oxygen functional groups such as carboxyls,epoxides, and alcohols, GO is hydrophilic and can readily exfoliate assingle sheets when ultrasonicated in H₂O. See Stankovich et al.,“Synthesis of graphene-based nanosheets via chemical reduction ofexfoliated graphite oxide” Carbon, 45, 1558 (2007). The average size ofan individual GO sheet after oxidation and suspension in H₂O may be 1μm² or less, with a thickness of approximately 1 to 1.5 nm.

Graphene oxide may be reduced back to graphene by the removal of theoxygen function groups and recovery of the aromatic double-bonded carbonstructure. Chemical reduction using hydrazine hydrate demonstrates thatthe conductivity of GO flakes can be increased by four- to five-ordersof magnitude. See Gilje et al., “A Chemical Route to Graphene for DeviceApplications” Nano Lett., 7, 3394 (2007). In addition, the mobility ofreduced flakes exhibit field effect mobilities between 2 to 200 cm²/V·s.See Gomez-Navarro et al., “Electronic Transport Properties ofIndividually Chemically Reduced Graphene Oxide Sheets” Nano Lett., 7,3499 (2007). The reduction of graphene oxide may not always be complete,however, and the product, reduced graphene oxide (r-GO), may retain acertain number of oxidized carbons that retain oxygen or oxygenfunctional groups. Thus, in a strict sense, r-GO may not be atomicallysimilar to pure graphene, though for applications, the two may beconsidered functionally equivalent.

Graphene is an allotrope of carbon in the form of a two-dimensional,atomic-scale hexagonal lattice in which one atom forms each vertex.Graphene is approximately 200 times stronger than steel by weight andconducts heat and electricity with great efficiency. It is the basicstructural element of other allotropes including graphite, charcoal,carbon nanotubes, and fullerenes. Carbon nanotubes are formed by rollingup a graphene sheet into a tubular structure, and graphite is formed bystacking multiple graphene sheets. Graphene or other allotropes ofcarbon may be synthesized and formed into a variety of morphologies andshapes including, but not limited to, nanoparticles, nanosheets,nanoplatelets, nanocrystals, nanospheres, nanowires, nanofibers,nanoribbons, nanorods, nanotubes, nanocylinders, nanogranules,nanowhiskers, nanoflakes, nanofoils, nanopowders, nanoboxes, nanostars,tetrapods, nanobelts, nanoflowers, etc. and mixtures thereof.

Structurally, graphene is a crystalline allotrope of carbon with2-dimensional properties. As used herein, graphene is a sheet ofsix-membered carbon rings that do not form a closed surface. Its carbonatoms are densely packed in a regular atomic-scale “chicken wire”(hexagonal) pattern. Each atom has four bonds, one σ-bond with each ofits three neighbors, and one π-bond that is oriented out of the plane.Graphene's hexagonal lattice can be regarded as two interleavingtriangular lattices.

Graphene's stability is due to its tightly packed carbon atoms and eachcarbon atom in a graphene sheet having an sp² orbital hybridization withdelocalized electrons present at opposite surfaces of the graphenesheet. The sp² hybridization is a combination of orbitals S, P_(x), andP_(y) that constitute the σ-bond, and the final P_(z) electron makes upthe π-bond. The π-bonds hybridize together to form the π-band and theπ*-band. These bands are responsible for most of graphene's notableelectronic properties, via the half-filled band that permits free-movingelectrons. Graphene is a zero-gap semiconductor. Graphene is also theonly form of carbon in which every atom is available for chemicalreaction from two sides due to the 2D structure.

The r-GO of the present invention may comprise less than 15 mol %carbon, preferably less than 5 mol % carbon, more preferably less than 3mol % carbon involved in a structural or chemical defect, including, butnot limited to isotopic impurities, substitutional impurities,vacancies, and interstitial impurities.

In one embodiment, the r-GO of the present disclosure has an oxygencontent of less than 5 wt %, preferably less than 4 wt %, preferablyless than 3 wt %, preferably less than 2 wt %, preferably less than 1 wt% relative to a total weight of the r-GO. In one embodiment, the r-GO ofthe present disclosure has a C/O ratio of at least 10, preferably atleast 20, preferably at least 30, preferably at least 40, preferably atleast 50, preferably at least 75, preferably at least 100, preferably atleast 150, preferably at least 200. In one embodiment, the r-GO may havea C/O ratio of less than 10, preferably less than 5, preferably lessthan 4, preferably less than 3, preferably less than 2.

In one embodiment, the r-GO of the present disclosure may be chemicallymodified; graphene is commonly modified with nitrogen and oxygencontaining functional groups. For instance, the r-GO may be formed fromgraphene oxide that is only partially reduced. Exposed carbon on theedges of nanosheets or nanoplatelets often reacts with the atmosphere toform hydroxyls, carboxyls, lactones, pyrones, alcohols, carbonyls,imines, and/or amines. These modifications may be covalent,non-covalent, or mixtures thereof. Examples of functional groups on r-GOinclude, but are not limited to, alcoholic, carboxylic, aldehydic,ketonic, and esteric oxygenated functional groups. Alternatively, ther-GO may be chemically modified with amine or imine functionality.Chemical functionalization of the r-GO may aid the adsorption/absorptionof different liquids, or improve the interface between the r-GO and thepolyurethane foam and/or the polystyrene.

In one embodiment, the r-GO of the present disclosure is in the form ofnanoplatelets that have a thickness of 40-110 nm, preferably 45-105 nm,more preferably 50-100 nm, or a thickness of 0.5-30 nm, 1-2 nm, or 1-1.5nm, and diameters of 5-45 μm, preferably 10-40 μm, more preferably 15-35μm. In one embodiment, the r-GO nanoplatelets have a length to thicknessaspect ratio of 40:1-1,200:1, preferably 50:1-1,000:1, more preferably70:1-900:1. Nanoplatelets having dimensions as discussed above may alsobe referred to as sheets, nanosheets, nanoflakes, nanoparticles, orplatelets. In an alternative embodiment, a different carbonaceousnanomaterial may be used in place of the r-GO nanoplatelets, such ascarbon black (e.g., furnace black and Ketjen black), active carbon,carbon nanorods, carbon nanotubes, carbon fibers, graphene, graphite,expandable graphite, graphene oxide, exfoliated graphite nanoplatelets,thermally reduced graphene oxide, chemically reduced graphene oxide, andmixtures thereof. In another embodiment, the r-GO of the presentdisclosure may be in the form of sheets having a thickness of 0.5-1.5nm, or less than 1.5 nm, and having lengths in a range of 50 nm-40 μm,preferably 70 nm-10 μm, more preferably 0.1-5 μm, or 0.5-2 μm. In somecases, two or more sheets of r-GO may be twisted, stuck, or bundledtogether, leading to a greater combined thickness and/or combinedlength.

In one embodiment, the layer of r-GO further comprises carbonnanoparticles having an average diameter in a range of 1-2 μm,preferably 1.1-1.9 μm, more preferably 1.2-1.8 μm, though in someembodiments, the layer may further comprise carbon nanoparticles havingan average diameter of less than 1 μm or greater than 2 μm. Thenanoparticles may have a spherical shape, or may be shaped likecylinders, boxes, spikes, flakes, plates, ellipsoids, toroids, stars,ribbons, discs, rods, granules, prisms, cones, flakes, platelets,sheets, or some other shape. In one embodiment, the carbon nanoparticlesmay be substantially spherical, meaning that the distance from thenanoparticle centroid (center of mass) to anywhere on the nanoparticleouter surface varies by less than 30%, preferably by less than 20%, morepreferably by less than 10% of the average distance.

In one embodiment, the carbon nanoparticles may be present withinagglomerates. As used herein, the term “agglomerates” refers to aclustered particulate composition comprising primary particles, theprimary particles being aggregated together in such a way so as to formclusters thereof, at least 50 volume percent of the clusters having amean diameter that is at least 2 times the mean diameter of the primaryparticles, and preferably at least 90 volume percent of the clustershaving a mean diameter that is at least 5 times the mean diameter of theprimary particles. The primary particles may be the carbon nanoparticleshaving a mean diameter as previously described.

In one embodiment, the layer of r-GO further comprises carbon nanotubesat a weight percentage of 5-80 wt %, preferably 10-60 wt %, morepreferably 12-20 wt %, relative to a total weight of the r-GO. In someembodiments, the layer of r-GO may comprise greater than 80 wt % carbonnanotubes. However, in another embodiment, the composite material doesnot contain carbon nanotubes, or may contain less than 1 wt % carbonnanotubes, preferably less than 0.2 wt % carbon nanotubes, relative to atotal mass of carbon.

In one embodiment, the layer of r-GO has an average thickness of 500nm-4.5 μm, preferably 1-4 μm, more preferably 1.5-3.5 μm on thepolyurethane surface. However, in some embodiments, the layer of r-GOmay have an average thickness of less than 500 nm or greater than 4.5μm. In one embodiment, the r-GO may form a disorganized, dense meshworkwhere only 0.5-5%, preferably 1-3% of the r-GO sheets, relative to thetotal number of r-GO sheets, directly contact the polyurethane surface.In one embodiment, at least 70%, preferably at least 75%, morepreferably at least 80%, or at least 85% or at least 90% or at least 95%of a total surface of the polyurethane foam is coated with the layer ofr-GO. In one embodiment, due to the adsorption of the r-GO in thepreparation of the composite material, the r-GO may comprise sheets ornanoplatelets that generally lay flat against the nearest surface of thepolyurethane foam structure. In a related embodiment, the sheets ornanoplatelets do not protrude from the polyurethane surface. Sheets ornanoplatelets of r-GO, even those attached from or in contact by onlyone end to the polyurethane surface, may be attached at an angle orattached substantially perpendicularly (i.e. forming an angle 70°-110°with the polyurethane surface) and then curved or bent to lay flat.

In one embodiment, the layer of r-GO may have a bulk density of0.001-1.0 g/cm³, preferably 0.005-0.20 g/cm³, more preferably 0.01-0.15g/cm³. In one embodiment, the layer of r-GO may comprise sheets ornanoplatelets having curved portions having a radius of curvature of 100nm-5 μm, preferably 500 nm-4 μm, more preferably 900 nm-3 μm.

As mentioned previously, the composite material comprises a layer ofpolystyrene in contact with the layer of r-GO. Styrene, also known asethenylbenzene, vinylbenzene, and phenylethene, is an organic compoundwith the chemical formula C₆H₅—CH═CH₂. This derivative of benzene is acolorless oily liquid that evaporates easily and has a sweet smell,although high concentrations have a less pleasant odor. Styrene is theprecursor to polystyrene and several copolymers. For instance, thepresence of the vinyl group allows styrene to polymerize. Commerciallysignificant products include polystyrene, ABS, styrene-butadiene (SBR)rubber, styrene-butadiene latex, SIS (styrene-isoprene-styrene), S-EB-S(styrene-ethylene/butylene-styrene), styrene-divinylbenzene (S-DVB),styrene-acrylonitrile resin (SAN), and unsaturated polyesters used inresins and thermosetting compounds. In the present disclosure, thecomposite material comprises a polystyrene layer.

Polystyrene results when styrene monomers interconnect. In thepolymerization, the carbon-carbon π bond of the vinyl group is brokenand a new carbon-carbon σ bond is formed, attaching to the carbon ofanother styrene monomer to the chain. The newly formed σ bond isstronger than the π bond that was broken, thus it is difficult todepolymerize polystyrene. About a few thousand monomers typicallycomprise a chain of commercially available polystyrene, giving amolecular weight of 100-400 kDa. The polystyrene of the polystyrenelayer herein may have a weight average molecular weight, or a numberaverage molecular weight, in a range of 0.4-400 kDa, preferably 0.5-300kDa, more preferably 0.6-200 kDa.

In one embodiment, at least 70%, preferably at least 75%, morepreferably at least 80%, or at least 85%, 90% of a total exposed surfaceof the composite material is the layer of polystyrene. In someembodiments, the polystyrene layer may be disjointed or continuous. Thepolystyrene layer may be in contact with parts of the polyurethane foamin some locations and in contact with the r-GO layer in other locations.In one embodiment, the polystyrene layer may only be in contact with ther-GO layer. In another embodiment, where the total exposed surface ofthe composite material comprises less than 100% polystyrene, theremaining exposed surface may comprise r-GO, polyurethane, or both. Inone embodiment, the layer of polystyrene and r-GO covers 50-90%, morepreferably 60-80%, even more preferably 70-80% of the polyurethanesurface area, meaning that from a certain view angle normal to thepolyurethane surface, only 10-50%, preferably 20-40%, even morepreferably 20-30% of the polyurethane surface is visible.

In one embodiment, the polystyrene layer may add a rough or wavy texturethat does not exist on an underlying r-GO or polyurethane surface. Forinstance, the polystyrene layer may create the appearance of zig-zagshaped ridges that are noticeable by the naked eye, as illustrated inFIG. 7E. For instance, the zig-zag shaped ridges may comprisesubstantially linear segments having an average length in a range of0.2-3 mm, preferably 0.5-2.5 mm, more preferably 0.8-2.0 mm. Thesesubstantially linear ridges may then connect end-to-end orend-to-midsection with other ridges, forming average acute angles in arange of 20°-60°, preferably 25°-55°, more preferably 30°-50°.

Additionally, under SEM imaging, as in FIGS. 4E and 4F, the polystyrenelayer may create additional wavy surfaces on the polyurethane/r-GOscaffold that have spacing in a range of 10-50 μm, preferably 20-45 μm.

In one embodiment, the layer of polystyrene has an average thickness of500 nm-4.5 μm, preferably 1-4 μm, more preferably 1.5-3.5 μm on the r-GOand/or polyurethane surface. However, in some embodiments, the layer ofpolystyrene may have an average thickness of greater than 4.5 μm. In oneembodiment, the polystyrene layer may comprise at least 95 wt %,preferably at least 98 wt %, more preferably at least 99 wt %polystyrene. In another embodiment, the polystyrene layer may comprise0-3 wt % or 0.01-0.50 wt % styrene monomer. In other embodiments,styrene derivatives other than polystyrene, such as those previouslymentioned, may be used in place of or instead of polystyrene in thecomposite material.

In an alternative embodiment, other polymeric compounds may be used inplace or with the polystyrene. Suitable polymers may be selected fromthe group including, but not limited to, polyacrylates, acrylics,poly(acrylic acid), poly(acrylonitrile),poly(2-hydroxyethylmethacrylate), sodium polyacrylate, ethylene glycoldimethacrylate, poly(vinyl pyridine), poly(methyl acrylate),polymethacrylates, poly(methyl methacrylate), polychloroprene,polyacrylamide, poly(N-isopropylacrylamide), poly(tetrafluoroethylene)(PTFE), poly(N-vinyl pyrrolidone), poly(vinyl pyrrolidinone), poly(vinylpyridine), polyethylenes, low-density poly(ethylene), high-densitypoly(ethylene), chlorinated polyethylene (CPD), poly(propylene),poly(isobutylene), poly(butylene), polyvinyl chlorides (PVC), polyvinylchloride acetate, polyacrylonitriles, poly(ethyl acetate), poly(vinylacetate), polyvinylacetates, polyvinyl acetate phthalate, ethylene vinylacetates, poly(ethylene glycol), polyphenylene ethers, poly(ethylenevinyl alcohol), poly(vinylidene fluoride), poly(p-phenylenevinylene),poly(benzoxazole), polyphenylenebenzobisoxazole (PBO),polyaryletherketones, poly(ether ether ketones), polyphenylenesulfides,polyamide imides, polyarylates, polyarylsulphones, ethyl-vinyl-alcoholcopolymers, copolymers of ethylene and 1-alkenes, polybutene-1,polymethylpentene, amorphous poly-alpha-olefins (APAO), terephthalates,polyacetylene, polyethylene oxides, polycycloolefins, polyisoprenes,polyamides, poly(ethylene terephthalate), poly(trimethyleneterephthalate), poly(butylene terephthalate), polycarbonates,polychlorotrifluoroethylene, polyvinyldifluoride, polyperfluoroalkoxy,poly(ethylene oxide), ethylene oxide copolymers, poly(ethylene imine),poly(dimethyl siloxane), polysiloxanes, fluorosilicones, fluoropolymers,polybutadienes, butadiene copolymers, epoxidized natural rubbers, epoxypolymer resins, poly (cis-1,4-isoprene), poly (trans-1,4-isoprene),viton, phenolic resins, acrylic resins, vinylacetate resins,polyurethanes, polyurethane-urea, thermosetting polyimides,thermoplastic polyimides, poly(amic acid), polysulfones,polyetherimides, polyethersulfones, chlorosulfonates, polyoxymethylene,polyphenylene oxide, polyphenylenes,perfluorinatedpolyethylenepropylene, polyvinylidene chloride,fluoropoly(ether-imide), polyolefins, aromatic polyamides (Aramid,para-aramid), polyesters, conducting and conjugated polymers, liquidcrystal polymers, liquid crystalline polyesters, vectran, biodegradablethermoplastic polyesters and their copolymers, thermosetting polyesters,unsaturated polyesters, acetals, fluorinated elastomers, rubbers,bismaleimides, copolymer rubbers, ethylene-propylene,ethylene-propylene-diene monomers (EPDM), nitrile-butadienes, nylons,thermoplastic continuous and discontinuous fiber composites,thermosetting continuous and discontinuous fiber composites, specialtypolymers, and blends, mixtures, alloys, and copolymers thereof.

According to a second aspect, the present disclosure relates to a methodof making the composite material of the first aspect, comprising thesteps of contacting a polyurethane foam with a suspension of r-GO in analcohol to produce a wet scaffold, drying the wet scaffold to produce ar-GO grafted polyurethane composite, and irradiating the r-GO graftedpolyurethane composite in the presence of a styrene vapor to produce thecomposite material.

The suspension of r-GO refers to a dispersed or solubilized mixture ofr-GO which does not settle. In a further embodiment, the suspension doesnot settle even with centrifugation. In one embodiment, the r-GO ispresent in the suspension at a concentration of 0.1-5 mg/mL, preferably0.2-3 mg/mL, more preferably 0.3-1 mg/mL, or about 0.5 mg/mL. Thesuspension may be made by contacting the r-GO with a solvent, such as analcohol, in order that the r-GO may be dispersed in the alcohol.

In one embodiment, the r-GO is dispersed in an alcohol which may bebenzyl alcohol, cyclohexanol, pentyl alcohol, phenol, 1-propanol,methanol, ethanol, butanol, isopropanol, or mixtures thereof. Preferablythe alcohol is methanol, ethanol, butanol, or isopropanol. In apreferred embodiment, the alcohol is ethanol.

In other embodiments, other solvents and liquids may be used for formingthe r-GO suspension. The solvent may be organic or aqueous, such as, forexample, water, chloroform, chlorobenzene, water, acetic acid, acetone,acetonitrile, aniline, benzene, benzonitrile, bromobenzene, bromoform,carbon disulfide, carbon tetrachloride, cyclohexane, decalin,dibromethane, diethylene glycol, diethylene glycol ethers, diethylether, diglyme, dimethoxymethane, N,N-dimethylformamide, ethylamine,ethyl benzene, ethylene glycol ethers, ethylene glycol, ethylene glycolacetates, propylene glycol, propylene glycol acetates, ethylene oxide,formaldehyde, formic acid, glycerol, heptane, hexane, iodobenzene,mesitylene, methoxybenzene, methylamine, methylene bromide, methylenechloride, methylpyridine, morpholine, naphthalene, nitrobenzene,nitromethane, octane, pentane, terpineol, texanol, carbitol, carbitolacetate, butyl carbitol acetate, dibasic ester, propylene carbonate,pyridine, pyrrole, pyrrolidine, quinoline, 1,1,2,2-tetrachloroethane,tetrachloroethylene, tetrahydrofuran, tetrahydropyran, tetralin, tetramethylethylenediamine, thiophene, toluene, 1,2,4-trichlorobenzene,1,1,1-trichloroethane, 1,1,2-trichloroethane, trichloroethylene,triethylamine, triethylene glycol dimethyl ether,1,3,5-trimethylbenzene, m-xylene, o-xylene, p-xylene,1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene,1,2-dichloroethane, N-methyl-2-pyrrolidone, methyl ethyl ketone,dioxane, or dimethyl sulfoxide. In certain embodiments of the presentinvention, the solvent may be a halogenated organic solvent such as1,1,2,2-tetrachloroethane, chlorobenzene, chloroform, methylenechloride, 1,2-dichloroethane, or chlorobenzene.

A preferred method of forming a suspension of r-GO is by sonication. Forexample, a given amount of r-GO is contacted or mixed with a givensolvent and subjected to sonication for a given period of time, forinstance, 5 min-2 h, preferably 10 min-1 h, more preferably 20-45 min,or about 30 min. The sonicator may be a bath sonicator or a sonicatinghorn or probe tip. In alternative embodiments, a different method offorming a suspension of r-GO may be used, for instance, media milling,shaking, or high-shear mixing. In one embodiment, cold water, such as bychilling with refrigeration or with ice, may be used as a bath to keepthe sonication from overheating the suspension.

Preferably the contacting involves completely submerging thepolyurethane foam within the suspension. For submerging, preferably aratio of the polyurethane foam bulk volume to the suspension volume is1:1,000-1:1, preferably 1:50-1:1, more preferably 1:5-1:1. The bulkvolume of the polyurethane foam may be considered the volume of itsconvex hull. However, dip-coating may be used with the polyurethane foambeing only partially submerged at any one time, but the foam may berotated to ensure an even coating.

In other embodiments, the contacting involves spraying, dropping thesuspension onto the polyurethane foam, injecting the suspension insidethe foam, or rotating the foam with the suspension. The polyurethanefoam may be compressed and then slowly expanded or decompressed whilecontacting in order to encourage a flow of the suspension to the insideof the foam. Particularly, when the polyurethane foam is submerged inthe suspension, compressing and decompressing the foam may drive out airbubbles by filling pores of the foam with the suspension.

In one embodiment, the contacting is done for a period of 3-60 min,preferably 3.5-45 min, more preferably 4-30 min, even more preferablyabout 5 min. However, in some embodiments, the contacting may be donefor a period of time much longer than 60 minutes, for instance, apolyurethane foam may be kept submerged in a r-GO suspension for 12-24hours, or overnight.

In one embodiment, the drying is at a temperature of 50-80° C.,preferably 55-75° C., more preferably 58-65° C., even more preferablyabout 60° C. for a period of 6-24 h, preferably 10-20 h, or about 12 h,18 h, or overnight. In another embodiment, the drying may be done at atemperature lower than 50° C., for instance, 40-45° C. In otherembodiments, a desiccator may be used. Following the drying period, ar-GO grafted polyurethane composite is produced. In one embodiment, ther-GO grafted polyurethane composite has a BET surface area in a range of5-20 m²/g, preferably 6-18 m²/g, more preferably 10-17 m²/g.

In one embodiment, the contacting and drying are each repeated one ormore times on the r-GO grafted polyurethane composite. For instance, thecontacting and drying may be repeated two more times or three moretimes. This repeated contacting and drying may increase the amount ofr-GO deposited on the composite by allowing additional r-GO to adsorb tothe existing layer of r-GO or to adsorb to uncovered regions ofpolyurethane. The repeated contacting may increase the BET surface areaof the composite by creating a thicker layer of r-GO.

As mentioned previously, the r-GO grafted polyurethane composite isirradiated in the presence of a styrene vapor to produce the compositematerial. The styrene vapor may have a vapor pressure in a range of 4-20mm Hg, preferably 6-15 mm Hg, more preferably 7-10 mm Hg within or incontact with the r-GO grafted polyurethane composite. In otherembodiments, 1-99 vol %, preferably 5-80 vol %, more preferably 6-70 vol% of the gas in contact with the r-GO grafted polyurethane composite maybe styrene vapor. Preferably the styrene vapor is produced from a volumeof liquid styrene in proximity to the r-GO grafted polyurethanecomposite. In one embodiment, the styrene vapor may be partiallyconfined by placing liquid styrene in the bottom of a tube or flask, andthen covering the opening of the tube or flask with the r-GO graftedpolyurethane composite. In one embodiment, the space above the r-GOgrafted polyurethane composite may also be covered. In a relatedembodiment, the r-GO grafted polyurethane composite may be locatedwithin a tubing. Preferably the r-GO grafted polyurethane composite hasa shape that is able to press against the sides of the tubing or flaskso that no gaps are present between a sidewall of the flask or tubingand the r-GO grafted polyurethane composite. This configuration mayforce any escaping styrene vapor to contact and pass through the r-GOgrafted polyurethane composite. In one embodiment, molecules of styrenemay adsorb to the exterior or interior surface of the r-GO graftedpolyurethane composite, and may be in direct contact with r-GO and/orpolyurethane.

In one embodiment, where liquid styrene is used, a volume ratio of theliquid styrene to the bulk volume of the r-GO grafted polyurethanecomposite may be in a range of 1:1,000-10:1, preferably 1:100-5:1, morepreferably 1:50-2:1, where the bulk volume of the r-GO graftedpolyurethane composite may be considered the volume of its convex hull.In one embodiment, a ratio of the headspace volume between the liquidstyrene and the r-GO grafted polyurethane composite and the r-GO graftedpolyurethane composite bulk volume may be in a range of 1:10-10:1,preferably 1:8-8:1, more preferably 1:5-5:1. In one embodiment, the bulkvolume of the r-GO grafted polyurethane composite may be 0.5-1,000 cm³,preferably 0.8-100 cm³, more preferably 1-20 cm³. In one embodiment, avolume of liquid styrene may be in a range of 0.5-10 mL, preferably 1-5mL, or about 3 mL.

In one embodiment, the liquid styrene, if present, the styrene vapor,and the r-GO grafted polyurethane composite are located withincontainers that are optically transparent, such as glass, quartz, orcertain plastics, so that the styrene vapor and r-GO graftedpolyurethane composite may be irradiated from an external source ofirradiation. The source of irradiation may be a flame, a lantern, a gasdischarge lamp (such as a xenon, sodium, or mercury vapor lamp), anincandescent bulb, a laser, a fluorescent lamp, an electric arc, a lightemitting diode (LED), a cathode ray tube, sunlight or some other sourceof light. Preferably the source of irradiation is sunlight. Anillumination power density of the irradiation may be in a range of40-200 mW/cm², preferably 80-150 mW/cm². Preferably the irradiation iswith one or more visible light wavelengths, or with a UV wavelength.

The irradiation may serve a dual purpose of producing styrene vapor byheating the styrene liquid, and also by initiating (photocatalyzing) thepolymerization of styrene into polystyrene. In alternative embodiments,a styrene liquid may be heated by other means to produce a vapor, forinstance, microwave-heating, a hot water bath, a steam bath, a heat gun,a heat lamp, a heating block, a heating mantle, an oven, a wire heatingelement, an ultrasonicator, or by other non-microwave electromagneticirradiation sources, such as an infrared laser. Preferably thetemperature of the styrene liquid remains below 80° C., preferably below70° C. or 60° C. Alternatively, in other embodiments, the liquid styreneand/or styrene vapor may be cooled in order to prevent overheating whenbeing exposed to sunlight and/or warm outdoor temperatures.

In one embodiment, the styrene must be adsorbed to the r-GO graftedpolyurethane composite in order to polymerize. In another embodiment,molecules of styrene vapor may begin to polymerize and then dimers,trimers, and other oligomers of styrene may adsorb to an interior orexterior surface of the r-GO grafted polyurethane composite. Adsorbeddimers, trimers, and other oligomers may continue to polymerize to formlarger molecules of polystyrene.

In one embodiment, a styrene or a polystyrene molecule adsorbed to ther-GO surface may covalently bond to the r-GO. For instance, thephotocatalyzing of the styrene and polystyrene may allow styrene andpolystyrene to form a covalent bond to the r-GO surface rather thangrowing a polymer chain. In one embodiment, during the irradiating, somestyrene and polystyrene may be polymerized while some may form covalentbonds to the r-GO. In one embodiment, a styrene or polystyrene thatforms a covalent bond to r-GO at one end is still able to polymerize atthe other end. At the end of the photocatalyzation process, there may bea mix of styrene and polystyrene molecules adsorbed to the r-GO surfacewith other styrene and polystyrene molecules covalent bond to the r-GOsurface. For instance, of the total number of styrene and polystyrenemolecules on the r-GO surface, 30-80%, 40-70% may be covalently bondedwhile the remaining percentage may be adsorbed without forming covalentbonds. In one embodiment, styrene and/or polystyrene may not adsorb aseasily or readily to pure graphene as compared with r-GO. In anotherembodiment, styrene and/or polystyrene may not form covalent bonds tothe surface of graphene as easily as to the surface of r-GO. In oneembodiment, the existing functionalities of r-GO, such as oxygencontaining groups, may provide places for the styrene and/or polystyreneto adsorb or form covalent bonds with.

In an alternative embodiment, a pure form of graphene may be used inplace of r-GO, though as mentioned previously, the resulting structureand degree of adsorption or covalent bonding may be different than withthe r-GO.

In one embodiment, the irradiating may be carried out for a time in arange of 10 min-24 h, preferably 15 min-4 h, more preferably 20 min-2 h.In one embodiment, the irradiating may be carried out for a time in arange of 10 min-4 h, preferably 15 min-3 h, more preferably 20 min-2 h,even more preferably 30 min-1.5 h, or 45 min-1 h, or 10 min-1 h. In oneembodiment, the irradiating may be performed continuously until theliquid styrene has completely vaporized. In another embodiment, the r-GOgrafted polyurethane composite may be rotated or the irradiation sourceor light path adjusted in order to irradiate from different sides.

In one embodiment, the method further comprises the step of contactingthe composite material with toluene after the irradiating. Here, thecomposite material may be submerged into toluene, or toluene may bepoured onto it. Then, the composite material may be immediately dried.The toluene may remove an amount of polystyrene from the compositematerial. Since excessive polystyrene may limit the compressibility ofthe composite material, the toluene may remove a portion of thepolystyrene in a way that increases the compressibility of the compositematerial. Having an increased compressibility may enable an increasedusability of the composite material. The toluene treatment may alsoincrease a weight gain ratio or adsorption capacity of the compositematerial. In one embodiment, the step of contacting with toluene mayremove 0.1-70 wt %, preferably 1-50 wt %, more preferably 2-35 wt %polystyrene relative to a total weight of the polystyrene before thecontacting. The composite material may be in contact with toluene for atime period of 2 s-5 min, preferably 5 s-1 min, more preferably 7 s-20s. In other embodiments, other solvents, such as those previouslylisted, may be used instead of toluene.

In a preferred embodiment, the entire method of making the compositematerial does not involve the use of silanes or a silanization reaction.In another embodiment, the entire method of making the compositematerial does not involve heating any materials at temperatures above80° C. In other embodiments, the heating is primarily used for thedrying step, and optionally, the styrene vaporization, thus, dryingtemperatures of 80° C., 70° C., 60° C., 50° C., or lower may set themaximum temperature involved in the entire process. In some embodiments,where the drying uses a desiccator at room temperature, the entiremethod may be carried out at temperatures of no greater than roomtemperature. In certain cases, while sonicating to form a suspension ofr-GO, active cooling may be required to maintain low maximum pressures.

According to a third aspect, the present disclosure relates to a methodof separating a nonpolar compound from an aqueous solution in a mixture.This involves contacting the mixture with the composite material of thefirst aspect, where the composite material adsorbs 8-25, preferably 9-22times, more preferably 10-20 times its weight of the nonpolar compound.In the context of this disclosure, the composite material adsorbing thenonpolar compound is considered equivalent to the composite absorbingthe nonpolar compound.

In one embodiment, the mixture may be a contaminated water mixture. Themixture may come from petroleum extraction or processing. In otherembodiments, the contaminated water mixture may come from an ocean, abay, a river, a lake, a swamp, a pond, a pool, a fountain, a bath, anaquarium, a water treatment plant, a sewage treatment plant, adesalination plant, a manufacturing plant, a chemical plant, a textileplant, a power plant, a gas station, a food processing plant, arestaurant, a dry cleaners, or some other place that may generatecontaminated water mixtures, or contaminated oil-water mixtures. In someembodiments, the contaminated water mixture may be in the form of anemulsion. In one embodiment, an aqueous dye or pigment may be used tovisualize the aqueous phase of the mixture without dying the nonpolarphase.

In one embodiment, the nonpolar compound may adopt a liquid state atroom temperature (20-27° C.). The nonpolar compound may be a linear orbranched alkane with a general formula of C_(n)H_(2n+2), where n mayhave a value of 5-18, preferably 10-17, more preferably 12-16. Inanother embodiment, the nonpolar compound may have a surface tension at19-22° C. of 10-50 mN/m, preferably 15-40 mN/m, more preferably 20-35mN/m. In other embodiments, the nonpolar compound may be some otherorganic molecule with a nonpolar or hydrophobic character and similarsurface tension. In other embodiments, the nonpolar compound may be amixture of organic molecules, for instance, a plant-based oil or apetroleum product such as mineral oil. In one embodiment, the nonpolarcompound is at least one selected from the group consisting of hexane,heptane, octane, toluene, xylene, and a petroleum-derived liquid. In oneembodiment, the nonpolar compound is a petroleum-derived liquid, such aspetrol (gasoline). In one embodiment, the nonpolar compound is hexane.

In another embodiment, other organic contaminants may be present ineither aqueous solution or as a nonpolar compound. The organiccontaminant may be an herbicide, a fungicide, a pesticide, apharmaceutical compound, a steroid, a microbial toxin, a metabolite, adisinfection byproduct, an arsenic-containing compound, a foodbyproduct, a dye, or some other organic molecule. Preferably thecontaminant is one or more unwanted compounds known as an environmentalpollutant.

In one embodiment, the mixture comprises the nonpolar compound at avolume percent concentration of 0.5-50%, preferably 2-45%, morepreferably 4-35% relative to a total volume of the mixture. The nonpolarcompound may be emulsified or dispersed throughout the mixture, mayfloat at the top of the mixture, or some combination of both. In analternative embodiment, the mixture may not contain oil or a non-polarliquid phase.

The mixture may comprise the aqueous solution at a volume percentconcentration of 50-99.5%, preferably 55-98%, more preferably 65-96%relative to a total volume of the mixture.

In one embodiment, a composite material may be reused for at least 3 or5 cycles, at least 10 cycles, or at least 15 cycles, with the weights ofthe nonpolar compound being adsorbed at each cycle having a relativestandard deviation (RSD) of 5% or less, preferably 4% or less, morepreferably 3% or less.

In some embodiments, the composite material may additionally adsorb asmall amount of aqueous solution with the contacting. Preferably thecomposite material adsorbs less than 20%, preferably less than 10%, morepreferably less than 5%, even more preferably less than 1% of its weightof the aqueous solution. In some cases, this small amount of aqueoussolution adsorption may be due to areas within the composite materialthat have exposed polyurethane without a layer of r-GO.

In one embodiment, the method further comprises the steps of compressingor squeezing the composite material after the contacting to produce adischarged (or used) composite and a volume of nonpolar compound andreusing the discharged composite. A used composite material may also becleaned or rinsed with solvents or other reagents before reuse. In someembodiments, a used composite material may be contacted again with ther-GO suspension and/or dried, prior to reuse. Alternatively, the usedcomposite material may be contacted again with styrene vapor andirradiated.

In a further embodiment, the discharged composite comprises at least 90wt %, at least 95 wt %, preferably at least 97 wt %, more preferably atleast 99 wt % r-GO relative to a total weight of r-GO in the compositematerial. In other words, the contacting and then compressing of thecomposite material results in a loss of less than 5 wt %, preferablyless than 3 wt %, more preferably less than 1 wt % of the initial weightof r-GO. A small or negligible loss of r-GO means that the compositematerial may be successfully reused multiple times, and preferably thereused composite material maintains an adsorption capacity that allowsthe composite to adsorb 20-50 times its weight of the nonpolar compound.However, in some embodiments, the adsorption capacity, in terms of theweight percentage of the nonpolar compound relative to a weight of thecomposite, may decrease by 2%, 1%, or by less than 1% with each usecycle.

In a related embodiment, the discharged composite comprises at least 90wt %, at least 95 wt %, preferably at least 97 wt % polystyrene relativeto a total weight of polystyrene in the composite material. Preferablythe discharged composite here had been treated to toluene as previouslymentioned in its method of making.

In one embodiment, the contacting involves filtering the mixture throughthe CNF grafted composite. The mixture may or may not be pre-processed,for instance, by filtering through a coarse filter to remove largeparticulate matter, or by exposure to UV light or ozone. Filtering themixture through the composite material means that a portion or all ofthe mixture passes through one area on an external surface of thecomposite material (the “feed side”), and that a permeate elutes andexits from some other area of the external surface of the composite (the“permeate side”). The composite material may be attached within a vesselor within a tubing, or at the end of a vessel or at the end of a tubing.Preferably, for filtering a polar and nonpolar phase-separated mixture,the feed side touches at least the nonpolar phase.

In one embodiment, the filtering leaves a retained aqueous phase that ismore than 90%, preferably more than 95%, more preferably more than 99%,even more preferably more than 99.5% of the total weight of the aqueousphase in the mixture before the contacting. The mixture may be filteredby the force of gravity, by siphoning, by pouring, or by applyingsuction or positive pressure.

In one embodiment of the filtering, a pressure difference across thefeed side to the permeate side of the composite material is 0-5 kPa,preferably 0-4 kPa, more preferably 0-3 kPa. Here, the pressuredifference may be created solely by the weight of a mixture on the feedside meaning that the filtration is gravity driven. Alternatively, thepressure difference may be created by a pump, a vacuum pump, a piston, acompressed gas, centrifugation, evaporation, or water jet aspiration.Preferably the pressure is constant, though in alternative embodiments,the pressure may be varied. In one embodiment, the nonpolar compoundpermeates through composite material at a flow speed of 0.5-20.0 mm/s,preferably 1.0-10.0 mm/s, more preferably 2.5-7.5 mm/s. In otherembodiments, flow speeds of 20-50 mm/s or greater than 50 mm/s may bepossible.

The examples below are intended to further illustrate protocols forpreparing, characterizing the composite material and uses thereof, andare not intended to limit the scope of the claims.

EXAMPLE 1 Experimental

Materials

Styrene was purchased from Alfa Aesar. Graphite was acquired from Fluka.Toluene and hexane were obtained from Merck and Sigma-Aldrich,respectively. Ethanol was obtained from Baker Analyzed® Reagent.Commercial polyurethane was purchased from a local market. Distilledwater was collected from a laboratory-based distillation unit.

Instrumentation

A MicromeriticsTriStar II Plus instrument was used for the measurementof the surface area and the pore size of the materials. A Goniometer wasused for the measurement of the contact angle. SEM images were recordedusing a scanning electron microscope. The FTIR of the materials werecollected using a Thermo Scientific Nicolet® iS10 instrument. Thematerial drying was done using a Blue M® oven. The stirring duringfabrication was done with the help of a Thermo-Scientific magneticstirrer.

Synthesis of Graphene

Graphene oxide (GO) was prepared using a modified Hummers method. See W.S. Hummers, et al., J. Am. Chem. Soc. 1859, 80, 1339. Briefly, theprocedure for the synthesis of GO is as follows. In a 500 mL volumetricflask, graphite powder (5 g) was added to 100 mL of concentratedsulfuric acid (H₂SO₄) and 100 g of sodium nitrate (NaNO₃). The resultingsolution was stirred for 30 minutes at 5° C. in an ice-bath. After that,potassium permanganate (KMnO₄) powder (15 g) was added slowly to theflask, and the mixture was heated to 35-40° C. and stirred for another30 minutes. Distilled water (200 mL) was then added to the above mixtureover a period of 25 minutes. Finally, 30% H₂O₂ was added to the mixtureuntil the formation of a yellowish solid product. The mixture was thenkept under stirring. The powder was separated in a centrifuge and washedseveral times by HCl solution and then by water. The obtained grapheneoxide was then reduced by sodium.

GO was reduced by using ascorbic acid. Around 20 g of ascorbic acid wasintroduced to the dispersed GO under stirring at 70° C. for 4 h. Theobtained material was allowed to cool and then separated in acentrifuge.

Fabrication of 3D zz-PS/GR/PU

A fine dispersion of 0.5 mg/mL graphene was prepared by sonicating thegraphene in ethanol for 1 hour. After sonication, a piece of PU wasdipped into the ethanol dispersed graphene. After that, it was removedfrom the ethanol dispersed graphene. It was dried and cured for 12 hoursin an oven at 60° C. The obtained graphene coated polyurethane wasdescribed as GR/PU. After the curing process, the GR/PU was transferredinto a glass reactor. The glass reactor contained 3 mL styrene monomer.In the glass reactor, the GR/PU was suspended almost in the middle toprevent it from touching the styrene liquid. Similarly, the PU withoutgraphene coating was also prepared in another glass reactor forperformance comparison. The glass reactors contained pure PU and theGR/PU was exposed to the natural sunlight until the styrene liquiddisappeared. The zigzag growth of the polystyrene on the GR/PU surfacewas observed clearly. After the polystyrene growth, the black color ofthe GR/PU was changed to blackish white. The achieved architecture ofthe 3D zigzag polystyrene/graphene incorporated polyurethane wasdescribed as 3D zz-PS/GR/PU. The 3D tzz-PS/GR/PU was obtained byinstantly dipping and then removing it from the pure toluene. After thistoluene treatment, it was dried at room temperature.

Experiment for Hexane/Water Separation

The experimental setup was designed for the hexane and water separation.The glass reactor in which the 3D zz-PS/GR/PU was synthesized was madeopen from both ends. It was directly fixed on the opening of thesuitable funnel to establish an experimental setup. The hexane and watermixture was prepared by mixing 100 mL hexane and 300 mL water in areagent bottle. The mixture was introduced through the separation setup.For the absorption experiment, the synthesized material was dipped intohexane and taken out for weight measurement.

EXAMPLE 2 Results and Discussion

Mechanism and Process of Trowing 3D zz-Polystyrene into GR/PU:

The synthesized hydrophobic material 3D zz-PS/GR/PU is a combination ofgraphene, polystyrene, and polyurethane. The incorporation of grapheneinto the polyurethane network provided a large surface area and alsocontributed to improving the mechanical properties of the material. Themidway hanging of the GR/PU into the glass reactor assisted withachieving uniform growth of PS in 3D zz-PS/GR/PU. The glass reactorplayed a crucial role in the formation of the 3D zz-PS/GR/PU. The glassreactor walls were transparent and permitted the sunlight radiation toenter the reactor through it. The synthesis process of 3D zz-PS/GR/PUwas completed in two-steps. The styrene liquid cannot approach directlyto the GR/PU because it is hanging midway in the middle of the reactor.The sunlight radiation entered into the transparent glass reactor whichprovided the heat to vaporize the volatile styrene and might also haveestablished an equilibrium between the styrene vapors and the liquidstyrene in the reactor. Vapors can move freely in the free space of thereactor and some of them stayed and passed through the porous network ofthe GR/PU. Simultaneously, the second step of polymerization wasstarted. During this step, the polymerization process of styrene wasinitiated by the natural light. In this polymerization step, the styrenevapors started to convert into polystyrene and further stimulated thestyrene liquid to vaporize. This process was continued until thepolymerization process was completed. FIG. 1 shows the two-step,sunlight initiated vaporization and polymerization of styrene.

The critical observation was made, after the polymerization ofpolystyrene on the pure polyurethane, that the interior of the PS/PUbecame fragile. It was shattered into small particles by touching itssurface. However, the incorporation of graphene into PU enhanced thegrowth of the polystyrene and the surface was more mechanically stable.The growth of polystyrene from the vapors of styrene is more interestingand provided a particular zigzag pattern of polystyrene which was porousin nature. This methodology might provide a better opportunity tocombine the intrinsic characteristics of the polyurethane, graphene, andpolystyrene for efficient utilization in various targeted fields. Thefabrication process for the 3D macro zigzag architecture of graphenereinforced polystyrene is illustrated in FIG. 2.

Surface Morphology and FTIR Study of the Materials:

The synthesized materials were characterized by transmission electronmicroscopy (TEM), scanning electron microscope (SEM) and Fouriertransfer infrared spectroscopy (FTIR). The synthesized graphene wascharacterized by the FTIR and the TEM. The FTIR spectra have shown thecharacteristic absorption peak of aromatic carbon-carbon double bond(—C═C—) at 1633 cm⁻¹. During the reduction process of graphene oxide,some oxygen-containing functionalities were retained which generallyappeared in the FTIR spectra of the reduced graphene oxide. Theabsorption peaks of oxygen-containing functionalities such as carboxy—C—O stretching (v=1391 cm⁻¹), alkoxy —C—O stretching (v=1027 cm⁻¹), andhydroxyl group (v=3438 cm⁻¹) absorption peaks appeared in the FTIRspectra of graphene. The TEM study revealed either one or only a fewlayered graphene. The FTIR and the TEM study have shown that graphenewas successfully synthesized (FIGS. 3A and 3B). The SEM images of thepure PU, PS/PU, and the 3D zz-PS/GR/PU were recorded at differentmagnifications to observe the morphological changes on the surface ofthe materials. The growth of the polystyrene on the surface of the purePU and GR/PU was seen clearly. The wrinkled shaped graphene was observedin the 3D zz-PS/GR/PU which was responsible for huge surface area andthe mechanical strength of the synthesized material (FIGS. 4A-4F).

The pure polyurethane FTIR spectra (FIG. 5) displayed itscharacteristics peaks. See S. Vlad, et al., e-Polymers 2009, 9, 1. Thevibrational absorption band appeared at 3225-3404 cm⁻¹ and 1541 cm⁻¹ wasassigned to —N—H stretching and —N—H deforming, respectively. The —CH₂symmetric and asymmetric stretching vibrational peaks appeared at 2866and 2970 cm⁻¹, respectively. The absorption peak appeared at 1450 cm⁻¹and was assigned to the —CH₂ bending vibration band. The peak whichappeared at 1714 cm⁻¹ in the spectra was assigned to the C═O vibrationalpeak. In the FTIR spectra of the polyurethane, the asymmetric stretchingvibrational peak of the NCO at 2270 cm⁻¹ was absent. The absence of theabsorption peak at 2270 cm⁻¹ revealed that after polymerization therewere no free NCO functionalities. See Y. Peng, et al., New J. Chem.2013, 37, 729; and H. B. Liu, et al., Key Eng. Mater. 2016, 703, 273. Astrong absorption peak was seen in the polyurethane spectra at 1097 cm⁻¹which was assigned to the stretching of C—O—C.

The introduction of polystyrene and graphene into the polyurethanebrought some obvious changes into the FTIR spectra, however, the basicstructure of the polyurethane was retained in the composite 3Dzz-PS/GR/PU (FIG. 5C). A substantial decrease in the peak intensity ofthe C—O—C was seen after the incorporation of graphene and the styrenepolymerization. It was shifted substantially from 1097 (PS/PU) to 1103cm⁻¹ (3D zz-PS/GR/PU). This interaction of the PU surface with thegraphene and the polystyrene might be responsible for the change in theC—O—C peak intensity and peak position. Apart from this, peak shifts inthe absorption peaks of the other functionalities were also observed. Ared shift in the —CH₂ symmetric and asymmetric peak of the PS/GR/PU wasobserved as the peaks shifted from 2866 to 2859 cm⁻¹ and 2970 to 2927cm⁻¹, respectively. A blue shift in the —N—H deforming peak was observedand it was shifted from 1541 to 1542 cm⁻¹. The carbonyl peak thatappeared in the pure polyurethane became considerably unclear in thePS/PU and PS/GR/PU FTIR spectra (FIG. 5).

Surface Area and Pore Size Evaluation of 3D zz-PS/GR/PU:

The utilization of nanomaterials in the synthesis of various compositescan bring some extraordinary properties into the material. It is evidentthat nanomaterials such as graphene have a substantial effect on thesurface area of the material. See N. Baig, A. Kawde, RSC Adv. 2016, 6,80756. In the absence of graphene, the pure PU surface area was found tobe 15 m²/g. The graphene incorporated 3D zz-PS/GR/PU showed substantialincremental growth in the surface area which increased from 15 to 67m²/g (FIG. 6A). The graphene and polystyrene also made a great impact onthe pore size of the material. The adsorption and desorption pore sizeof the pure PU was found to be 354 and 352 Å, respectively. After thegraphene and polystyrene incorporation, the 3D zz-PS/GR/PU pore size wassubstantially decreased to 34 and 33 Å (FIG. 6B). The incremental growthin surface area and the decrease in the pore size revealed that theremight be new pores and surfaces generated in the 3D zz-PS/GR/PU whichwere responsible for the surface area improvement. Furthermore, thedecrease in pore size provided better channels with superhydrophobicityfor the efficient separation of oil and water.

Surface Hydrophobicity

The synthesized 3D zz-PS/GR/PU hydrophobicity and the oleophilicity wereevaluated with the mixture of water and hexane. Both liquids arenaturally colorless and methylene blue colored water was used todifferentiate between the water and hexane. The growth of thepolystyrene is evidently observed from the upper view of the glassreactor (FIG. 7A). In the start of the reaction process, the styreneliquid was at the bottom of the glass reactor and therefore had nochance to come into direct contact with the GR/PU. The synthesis of thepolystyrene on the upper side of the 3D zz-PS/GR/PU was a clearindication that vapors of the styrene was passing easily through theGR/PU. The passage of vapors all-around the GR/PU was also evident fromthe side-wise growth of the polystyrene (FIG. 7C). After some detailedand comprehensive investigation of the surface, it was revealed thatthere was some sort of pattern in the growth of the polystyrene. Thispattern of polystyrene was spread all over the 3D composite. Thesewell-organized patterns appeared in a zigzag arrangement (FIG. 7E). Thissort of arrangement exposed more surface area and may provide some sortof hollow arrangement which allowed the rapid passage of the non-polarcomponent. The synthesized composite 3D zz-PS/GR/PU is superhydrophobicin nature and it can be seen in FIG. 7B where the methylene blue coloreddrop of water was fully retained by the surface. The drop of waterbecame entirely circular on the 3D zz-PS/GR/PU surface due to thesuperhydrophobic nature of the surface which did not allow the water tomake a significant contact with the surface in order to pass. All sidesof the zz-PS/GR/PU were scanned to observe its behavior towards thewater. This study has revealed that all sides of the zz-PS/GR/PU weresuperhydrophobic and did not allow the water to spread or pass throughit (FIG. 7B-7C).

The established 3D hydrophobic architecture was investigated for itsefficiency to separate the oil from water. The separation setup used canbe seen in A of FIG. 8. The water and hexane mixture was added from theupper part of the oil/water separation setup which contained the 3Dzz-PS/GR/PU in its upper part. Amazingly the 3D zz-PS/GR/PU exhibitedboth superhydrophobic and superoleophilic behavior. The hexane wasallowed to pass quickly simply under the force of gravity withoutapplying any external force, while the methylene blue colored water wasnot permitted to pass through the 3D zz-PS/GR/PU. The separation ofhexane and water was seen in the separating setup (B of FIG. 8) wherethe upper part of the glass reactor contained the methylene blue coloredwater while the hexane passed through it.

The synthesized 3D zz-PS/GR/PU composite was not compressible andappeared hard in nature. Due to its non-compressible nature, itexhibited a hard tube like capillary behavior which allows for the rapidgravity-driven passage of hexane. Due to its non-compressible nature, itcould not keep a large quantity of the hexane although it stillpossessed the absorption capability of the non-polar organic solvents.The weight gain ratio of the 3D zz-PS/GR/PU for hexane was found to be890%. This is an indication that it could take a good quantity of hexaneapart from its compact nature. The absorbed hexane can be releasedsimply by shaking the 3D-PS/GR/PU due to its weak holding capacity. Thesynthesized material has long-term stability and it can be used multipletimes without compromising its efficiency for hexane and waterseparation. It can be shown to be a valuable superhydrophobic materialfor the bulk separation of oil and water due to the rapid passage of oilthrough it.

Toluene Treated 3D zz-PS/GR/PU:

As mentioned previously, the zz-PS/GR/PU has a compact and stiff surfacewhich provides tube-like channels and allows for the rapid passage ofthe hexane through it. These channels were hydrophobic enough to preventwater from passing. Polystyrene showed some solubility in the toulene.See M. T. Garcia, et al., Waste Manag. 2009, 29, 1814. This interactionof the polystyrene and the toluene was used as a tool to produce thecompressable 3D tzz-PS/GR/PU. The toluene treatment showed some changein the weight of the material. The weight of the 3D tzz-PS/GR/PU wasfound to be 8.47% less compared to 3D zz-PS/GR/PU. This change in weightindicates that some of the polystyrenes dissolved into toluene whichbroke the continuous structure which imparted the compressible behaviourto the material. The compressible nature of the 3D tzz-PS/GR/PU is shownin FIG. 9, and it can be fully pressed between the fingers. Afterreleasing the pressure, it regained its original shape (FIG. 9). Thistreatment might have some affect on the hydrophobic behavior of the 3Dcomposite. For this reason, the hydrophobic behaviour of the 3Dtzz-PS/GR/PU was investigated using methylene blue colored water. It didnot allow the water to pass and the water droplet maintained samecircular shape on the 3D tzz-PS/GR/PU. The polystyrene on the surfacesomehow became fluffy (D of FIG. 9). Its capability to absorb hexane wassignificantly improved and the percent weight gain ratio of the 3Dtzz-PS/GR/PU was improved to 89% compared with 3D zz-PS/GR/PU (FIG. 10).The absorbed hexane is released from 3D tZZ-PS/GR/PU by squeezing. Thecomparison of the synthesized hydrophobic material was shown to beeither comparable or superior in efficiency to the reported hydrophobicmaterials in table 1.

TABLE 1 Comparison of the syntheized hydrophobic materials with otherreported hydrophobic material for hexane absorption. BET surface areaHexane Sr# Adsorbent (m²/g) (g/g) Recycling Ref. 1 Hydrophobic CNFaerogels 18.4  24 Evaporation (a) 2 multi-functional — 22 Distillation,(b) carbon fiber Combustion, Squeezing 3 Polydopamine/chitosan/ 51.76 12Squeezing, (c) reduced graphene Heating oxide composite aerogel 4 Cupricstearate/sponges — 22.63 (d) 5 Swellable porous — 15.05 squeezing (e)PDMS/MWNTs 6 Graphene aerogels 100-350 25 — (f) 7 CNT/PDMS-coated 15 (g)PU sponge 8 MTMS-DMDMS gels — 6 squeezing (h) 9 3D zz-PS/GR/PU 67   9Evaporation, This Shaking, work 10 3D tzz-PS/GR/PU — 17 Squeezing, ThisEvaporation work See (a) A. Mulyadi, et al., ACS Appl. Mater. Interfaces2016, 8, 2732; (b) S. Yang, et al., RSC Adv. 2015, 5, 38470; (c) N. Cao,et al., Chem. Eng. J. 2017, 326, 17; (d) Z. Liu, et al., RSC Adv. 2016,6, 88001; (e) A. Turco, et al., J. Mater. Chem. A 2015, 3, 17685; (f) J.Wang, et al., J. Mater. Chem. 2012, 22, 22459; (g) C.-F. Wang, et al.,ACS Appl. Mater. Interfaces 2013, 5, 8861; and (h) G. Hayase, et al.,Angew. Chemie Int. Ed 2013, 52, 1986.

Overall, a cost-effective method was introduced for the fabrication ofsuperhydrophobic 3D zz-PS/GR/PU material. The 3D superhydrophobicarchitecture was accomplished by initiating the polymerization ofstyrene with the help of natural sunlight containing graphene andpolyurethane in a confined glass reactor. The polymerization processproduced a well-decorated pseudo zigzag arranged polystyrene pattern onthe GR/PU. The incorporation of graphene into PU provided a huge surfacearea and also mechanical stability to the material. In the grapheneincorporated PU, the polystyrene patterns and growth were more prominentcompared to pure PU. This might be due to the better surface area andthe catalytic effect of the graphene. The 3D zz-PS/GR/PU provided thecompact porous superhydrophobic channels for the rapid gravity drivenseparation of oil and water, whereas the 3D tzz-PS/GR/PU is acompressible material with a high absorbing capability for hexane. The3D zz-PS/GR/PU and 3D tzz-PS/GR/PU showed a hexane absorption capacityof 9 and 17 g/g, respectively. The 3D zz-PS/GR/PU displayed a highsurface area of 67 m²/g with a small adsorption and desorption pore sizeof 34 and 33 Å, respectively. The water contact angle displayed by the3D zz-PS/GR/PU was approximately 150°. In separated hexane apparently,no water was found and it had an almost 100% capacity to separate hexanefrom water. This route of formation can provide a cost-effectiveapproach to produce a hydrophobic material on a large scale which isgenerally a challenging task, especially on a laboratory scale. Thedeveloped methodology of synthesis is exceedingly robust andreproducible. It may encourage researchers to look for other polymersand nanomaterials for the fabrication of a 3D porous architecture forvery demanding applications in the fields of energy, oil/water,supercapacitors, and sensors.

1: A composite material, comprising: a polyurethane foam coated with alayer of reduced graphene oxide (r-GO), and a layer of polystyrene incontact with the layer of r-GO, wherein the composite material has porediameters in a range of 50-500 μm. 2: The composite material of claim 1,wherein an apparent contact angle with water is 130°-170°. 3: Thecomposite material of claim 1, having an adsorption pore size in a rangeof 25-50 Å. 4: The composite material of claim 1, having a BET surfacearea in a range of 50-100 m²/g, 5: The composite material of claim 1,wherein at least 70% of a total surface of the polyurethane foam iscoated with the layer of r-GO. 6: The composite material of claim 1,wherein at least 70% of a total exposed surface of the compositematerial is the layer of polystyrene. 7: A method of making thecomposite material of claim 1, comprising: contacting a polyurethanefoam with a suspension of r-GO in an alcohol to produce a wet scaffold;drying the wet scaffold to produce a r-GO grafted polyurethanecomposite; and irradiating the r-GO grafted polyurethane composite inthe presence of a styrene vapor to produce the composite material. 8:The method of claim 7, further comprising contacting the compositematerial with toluene after the irradiating. 9: The method of claim 7,wherein the polyurethane foam has a BET surface area in a range of 5-20m²/g. 10: The method of claim 7, wherein the r-GO grafted polyurethanecomposite has a BET surface area in a range of 5-20 m²/g. 11: The methodof claim 7, wherein the r-GO is present in the suspension at aconcentration of 0.1-5 mg/mL. 12: The method of claim 7, wherein thedrying is at a temperature of 50-80° C. for a period of 6-24 h. 13: Themethod of claim 7, wherein the irradiating involves exposing the r-GOgrafted polyurethane composite to sunlight. 14: A method of separating anonpolar compound from an aqueous solution in a mixture, the methodcomprising: contacting the mixture with the composite material of claim1, wherein the composite material adsorbs 8-25 times its weight of thenonpolar compound. 15: The method of claim 14, wherein the nonpolarcompound is at least one selected from the group consisting of hexane,heptane, toluene, xylene, and a petroleum-derived liquid. 16: The methodof claim 14, wherein the composite material adsorbs less than 20% of itsweight of the aqueous solution. 17: The method of claim 14, wherein thecontacting involves filtering the mixture through the compositematerial. 18: The method of claim 14, further comprising: compressingthe composite material after the contacting to produce a dischargedcomposite material, and reusing the discharged composite material. 19:The method of claim 18, wherein the discharged composite materialcomprises at least 90 wt % r-GO relative to a total weight of r-GO inthe composite material. 20: The method of claim 18, wherein thedischarged composite material comprises at least 90 wt % polystyrenerelative to a total weight of polystyrene in the composite material.